Parameters

Revit provides a general mechanism for giving each element a set of parameters that you can edit. In the Revit UI, some element parameters are visible in the Element Properties Palette. This section describes how to get and use built-in parameters using the Revit Platform API. For more information about user-defined shared parameters, see Shared Parameters.

In the Revit Platform API, Parameters are managed in the Element class. You can access Parameters in these ways:

By iterating through the Element.Parameters collection of all parameters for an Element (for an example, see the sample code in Walkthrough Get Selected Element Parameters).
By iterating through the collection returned by Element.GetOrderedParameters(), which returns only parameters visible in the Properties Palette.
By accessing the parameter directly through the overloaded Element.Parameter property. If the Parameter doesn't exist, the property returns null.
By accessing a parameter by name via the Element.ParametersMap collection.
By name string Element.LookupParameter() or Element.GetParameters().

You can retrieve the Parameter object from an Element using the overloaded Parameter property if you know the built-in ID, definition, or GUID. The Parameter[GUID] property overload gets a shared parameter based on its Global Unique ID (GUID), which is assigned to the shared parameter when it's created.

The Element.LookupParameter() method gets a parameter based on its localized name, so your code should handle different languages if it's going to look up parameters by name and needs to run in more than one locale. Also, keep in mind that multiple matches of parameters with the same name can occur because shared parameters or project parameters can be bound to an element category even if there is already a built-in parameter with the same name. For this reason, it is better to use Element.GetParameters() which will return all parameters matching the given name. Element.LookupParameter() will return the first match found.